The role of semaphorins in lung cancer

The semaphorins are a family of secreted, transmembrane, and membrane-associated proteins initially identified as causing the repulsion of nerve growth cone guidance. However, subsequent experiments have demonstrated that they can induce retraction in non-neural cells and affect the development of non-neural organs. Two related secreted semaphorins, SEMA3F and SEMA3B, were isolated from a recurrent 3p21.3 homozygous deletion region in small-cell lung cancer (SCLC) cell lines. Moreover, a functionally related molecule, Roundabout/DUTT1, was identified as the target of a more proximal chromosome 3p deletion also involving SCLCs. Based on current data, it is likely that the loss of these semaphorins or Roundabout may affect cell migration, metastasis, and apoptosis. In addition, receptors for the secreted semaphorins, neuropilin-1 and neuropilin-2, have been shown to function as coreceptors for a subset of vascular endothelial growth factor (VEGF) isoforms and related growth factors. Since semaphorins and VEGF bind antagonistically to neuropilins, their loss is likely to facilitate angiogenesis. In lung cancer specimens, antibody staining against SEMA3F has been shown to correlate with stage and histologic subtypes with more aggressive tumors showing increased VEGF and decreased SEMA3F staining. This review is focused on a basic understanding of these pathways with an emphasis on their role in lung cancer.